What Happens During an Allergy Test?

If your doctor thinks you might have an allergy, you’ll probably go see an allergist (a doctor who diagnoses and treats allergies) for testing.

Here's what to expect. The allergist will ask questions like:

• What symptoms do you notice when you have a reaction? (e.g., hives or a scratchy throat)
• How often does the reaction happen?
• How long does it take between eating a particular food and the start of the symptoms?
• Do any family members have allergies or conditions like eczema and asthma?

The allergist will also do tests. Skin tests are a common way to diagnose allergies.

What Are Skin Tests?

In a typical skin test, an allergist or nurse will place a tiny bit of an allergen (such as pollen or food) on the skin, then make a small scratch or prick on the skin. Allergists usually do skin tests on a person's forearm or back. The allergist then waits 15 minutes or so to see if reddish, raised spots form, possibly indicating an allergy.

If a person might be allergic to more than one thing — or if it's not clear what's triggering a person's allergy — the allergist will probably skin test for several different allergens at the same time.

Skin tests may itch for a while. The allergist might give you antihistamine or steroid cream after the test to ease the itching.

When a skin test shows up as positive for a food, that only means a person might be allergic to that food. In these cases, doctors may want to do more testing.

What Other Tests Are Done to Look for Allergies?

To diagnose a food allergy for sure, an allergist may do a blood test in addition to skin testing. This involves taking a small blood sample to send to a lab for analysis. The lab checks the blood for IgE antibodies to specific foods. If there are many IgE antibodies to a particular food, the person is very likely to be allergic to it.

Doctors often use a combination of skin testing and blood testing to diagnose a food allergy.

If the results of the skin and blood tests are still unclear, though, an allergist might do something called a food challenge. During this test, the person gets slowly increasing amounts of the potential food allergen to eat while the doctor watches for symptoms.

Because food allergies can trigger serious reactions in people, this test must be done in an allergist's office or hospital that has access to medicines and specialists to control serious allergic reactions. Most of the time, this type of test is done to find out if someone has outgrown a known allergy.

What Happens if a Test Shows an Allergy?

If you do have an allergy, the doctor will work with you on a plan to keep you safe. Treatment depends on the allergy — for people with environmental allergies, this might mean avoiding triggers that make symptoms worse, taking medicine, or getting allergy shots. For a food allergy, the doctor will help you learn how to avoid foods that aren’t safe for you. The doctor will also give you a prescription for emergency medicine — called epinephrine  — to keep with you all the time in case of a severe allergic reaction.